This is the renewal of research project NS-09871, entitled Surgical Anesthesia and Pain Control - Neuropharmacology. The research projects proposed herein are extensions of the previous studies but with considerable departure from our past approaches, and are aimed at the activity of spinal-cord neurons, modulated by narcotic analgesics and anesthetics while physiological parameters of animals are maintained strictly within the normal range. The departure from our past approaches, as defined below, shows our new direction. Utilizing microelectrode single-unit recording techniques with the aid of a computerized statistical data analysis program available in our laboratory, we propose: (1) To analyze the direct effects of ankephalins and endorphins on spontaneous and heat-evoked activity of spinal-cord neurons in cats with transected spinal cords. (2) To analyze the effects of intrathecal administration of local anesthetics (conventional spinal anesthesia) and narcotic analgesics (newly developed spinal analgesia) on the spontaneous and heart-evoked activity of spinal-cord neurons in cats with transected spinal cords. (3) To analyze the importance of the activation of phasic descending inhibition induced by brain stimulation on the ability of narcotic analgestics to modify the spontaneous and heat-evoked activity of spinal-cord neurons in intact cats (without decerebration or spinal-cord transection) under basal narcosis. (4) To analyze the effects of narcotic analgesics and anesthetics upon the spontaneous and heat-evoked activity of spinal neurons in awake freely behaving cats in the absence of basal narcosis and/or decerebration, and to assess the overall role of spinal cord depression in drug induced analgesia. To stimulate surgical stimuli a thermal stimulus will be used.